The Oesophagus

Anatomy ( Table 19.1 )

The oesophagus is a fibromuscular tube that connects the pharynx in the neck to the stomach in the abdomen, traversing the thorax via the superior and posterior mediastinum. It begins below the cricopharyngeus muscle, at the lower edge of the cricoid cartilage and at the level of C6. In the neck, the oesophagus lies posterior to the trachea. As it descends through the mediastinum, it passes posterior to the aortic arch, the left main bronchus and the left atrium, each of which causes an impression ( Fig. 19.1 ). At the diaphragm the oesophagus passes through the diaphragmatic hiatus at T10, accompanied by the vagus nerves; it ends at the gastric cardia at the level of T11. The abdominal oesophagus lies posterior to the left lobe of the liver. The oesophagus is therefore composed of a short cervical, a long thoracic and a short abdominal segment.

In health, the oesophagus is lined by stratified non-keratinising squamous epithelium. At the gastro-oesophageal junction (GOJ) there is an abrupt transition to columnar epithelium, termed the ‘Z-line’ because of the irregular interdigitations between pale pink squamous and darker columnar epithelia ( Fig. 19.2 ). The GOJ is usually found at a surprisingly constant 40 cm from the teeth.

The wall of the oesophagus is made up of five layers: the mucosa, the muscularis mucosa, the submucosa, the muscularis propria and the adventitia.

Embryology

The stratified squamous epithelium of the oesophagus, together with its associated submucosal glands, is derived from the endoderm of the foregut. The striated muscle of the upper oesophagus is derived from branchial arches 4 and 6, whereas the smooth muscle of the lower oesophagus is derived from somite mesenchyme. The myenteric plexus is derived from neural crest cells.

Function

The oesophagus actively moves ingested material from the pharynx to the stomach and thus prevents reflux of stomach contents. Passage of a food bolus is regulated by the upper and lower oesophageal sphincters. The upper oesophageal sphincter is a high-pressure zone at the pharyngo-oesophageal junction and comprises the cricopharyngeus, the thyropharyngeus and the superior part of the cervical oesophagus. The lower oesophageal sphincter is a 3-cm-high pressure zone at the GOJ and is composed of the lower oesophageal muscle fibres and the diaphragmatic hiatus. The GOJ is anchored by the phreno-oesophageal ligament, which allows the oesophagus to slide a short distance longitudinally through the diaphragmatic hiatus while acting as a seal between the thoracic and abdominal cavities.

Unlike the upper and lower oesophageal sphincters, the oesophagus between these high-pressure zones is relaxed in the resting state. The swallowing reflex induces so-called primary peristaltic (or stripping) waves that travel at 3 to 4 cm/s. Secondary peristalsis occurs when oesophageal sensory receptors are activated by material persisting in the oesophagus after primary peristalsis. Tertiary contractions are non-propulsive and are seen in a variety of motility disorders ( Fig. 19.3 ).

Plain Radiography

In most circumstances, plain radiographs reveal little useful information regarding the oesophagus except in the context of foreign body ingestion. Foreign bodies tend to lodge at one of the following oesophageal constriction points:

• Cricopharyngeus

• Aortic arch

• Left main bronchus

• Diaphragmatic hiatus

Otherwise, a dilated, gas- or fluid-filled oesophagus ( Fig. 19.4A and B ) may be identified incidentally during chest radiography for other indications.

Ultrasound

Most of the oesophagus is inaccessible to conventional ultrasound examination (but see ‘Endoscopic Ultrasound’, later). The short cervical and abdominal segments are amenable to imaging in this way, but this is rarely used in clinical practice.

Fluoroscopy

Fluoroscopic examination of the oesophagus is performed for a wide variety of indications. Barium suspensions are preferred for most indications; a preparation of 100% w/v is often used to provide good mucosal coating and an appropriate density. If possible, double-contrast images should be obtained using an effervescent agent, usually with the patient in the erect position. These are complementary to prone, single-contrast images.

Water-soluble contrast medium is used when a tear, perforation or anastomotic leak is suspected. Low osmolar agents such as iopamidol (Gastromiro) should always be used to prevent pulmonary oedema, which can occur following aspiration of high osmolar agents such as meglumine diatrizoate (Gastrografin).

In some institutions, when a leak is suspected, water-soluble contrast medium is followed with a barium suspension. Using barium in this way has been shown to be more sensitive for contained perforations, although it adds nothing in the detection of free leakage into the neck or mediastinum.

Fluoroscopic examination of the oesophagus is tailored to the indication, but a suggested technique is as follows: control images should be obtained if the patient has had oesophageal or gastric surgery. With the patient in the erect position, double-contrast images are obtained in the lateral and posteroanterior (PA) projections of the cervical and upper oesophagus at four images per second. Right anterior oblique images of the middle and lower oesophagus are obtained at two per second, also in double contrast. The patient is then moved to the prone position and images are obtained at one per second during three separate single-bolus swallows to assess oesophageal motility and fully distend the GOJ. This view is particularly important if wrap migration is suspected following fundoplication. The images obtained in the prone position are usually single contrast. Finally, a static image of the stomach to include the gastric fundus is obtained with the patient in the erect position.

The standard fluoroscopic examination may be augmented with additional procedures. As an example, where a patient describes a clear history of dysphagia, but the images obtained appear normal, a swallow of biscuit dipped in barium or a barium tablet may uncover an occult stricture. If there are pharyngeal symptoms, images of the pharynx obtained during phonation should be obtained.

Although no longer the first-line test for dysphagia, fluoroscopy remains an important test. It is well suited to evaluate the oesophagus following trauma or surgery, in complex hiatal herniae and as a less invasive alternative to endoscopy in the frail patient ( Fig. 19.5 ).

Endoscopy

Oesophagogastroduodenoscopy (OGD/endoscopy) is the initial investigation of choice for most indications, particularly dysphagia. It permits the direct visualisation of the mucosa and, crucially, biopsies can be taken. In patients with high dysphagia, preliminary fluoroscopic assessment can be used to forewarn the endoscopist of a pharyngeal pouch, which if present, would potentially reduce the risk of perforation.

An OGD is carried out with the patient in the left lateral position, under topical local anaesthesia or conscious sedation (usually with a benzodiazepine such as midazolam). In addition to a detailed diagnostic assessment of the mucosa, a wide variety of therapeutic manoeuvres may be carried out endoscopically. These include the treatment of upper gastrointestinal (GI) haemorrhage, balloon dilatation and/or stenting of strictures, radiofrequency ablation (RFA) of dysplastic epithelium and injection of botulinum toxin for motility disorders. Endoscopic mucosal resection (EMR) deserves special note, as it is both therapeutic and the preferred method for staging early oesophageal tumours.

Computed Tomography

In the context of oesophageal disease, CT is most widely used in the staging of oesophageal cancer. A CT of the thorax, abdomen and pelvis should be acquired. Good oesophageal and gastric distension is important: the patient should be given 1–1.5 L of water to drink as well as effervescent granules and should be imaged in the prone position. Intravenous contrast medium should be used whenever possible, with the upper abdomen imaged in both the arterial and portal venous phases.

For the investigation of patients with suspected oesophageal trauma (including Boerhaave syndrome) and in the postoperative setting, positive oral contrast medium is required. As for fluoroscopic examinations, this should always be carried out with a low osmolar agent. For suspected tracheo-oesophageal fistula, an initial acquisition without the use of oral contrast medium is usually diagnostic ( Fig. 19.6 ).

Magnetic Resonance Imaging

In current clinical practice, magnetic resonance imaging (MRI) is not used for imaging the oesophagus. Image quality is hampered by motion artefacts from cardiac motion, breathing and peristalsis ( Fig. 19.7 ). Whole-body MRI is under evaluation as an alternative to PET-CT for the staging of metastatic disease in oesophageal cancer but has not yet entered clinical practice.

Endoscopic Ultrasound

EUS is generally used to characterise abnormalities identified using other imaging techniques, in particular the staging of oesophageal cancer. Less frequently, EUS is used for the assessment of submucosal lesions of the oesophagus. The high frequency and close proximity of the ultrasound probe allow the delineation of five layers of the oesophageal wall: mucosa, muscularis mucosa, submucosa, muscularis propria and adventitia. The muscular layers are hypoechoic; hence, there is a five-layered alternating pattern.

Endoscopic ultrasound/fine-needle aspiration (EUS-FNA) enables the sampling of structures deep to the oesophageal mucosa, particularly thoracic and upper abdominal lymph nodes. This can be particularly useful in the staging of oesophageal and lung malignancy and in the diagnosis of tuberculosis. In addition to sampling, EUS can be used to place fiducial markers to guide radiotherapy.

Radionuclide Radiology Including Positron-Emission Tomography–Computed Tomography

For patients with oesophageal cancer, ¹⁸ F-fluorodeoxyglucose (FDG) PET-CT is now the standard of care if radical treatment is intended. The presence of FDG-avid lymph nodes on preoperative PET-CT is prognostically significant even within the group of patients with the same pathological stage. The most important reason that PET-CT is used in oesophageal cancer staging is the high proportion of patients who have unsuspected metastatic disease at presentation ( Fig. 19.8 ) and the superiority of PET-CT over other techniques for identifying it.

Technetium-based radionuclide imaging of the oesophagus can be used for the identification of oesophageal motility disorders and gastro-oesophageal reflux disease (GORD). Patients can be imaged swallowing both liquid and solid material (usually ^99m Tc-labelled sulphur colloid and scrambled egg, respectively) ( Fig. 19.9 ).